The inbox setting can be overridden by returning {{{namespace/default/inbox=yes}}} extra field.

The inbox setting can be overridden by returning {{{namespace/default/inbox=yes}}} or {{{namespace/default/location=mbox:/var/mail/%u}}} extra field.

User database extra fields

A user database lookup typically returns uid, gid and home fields, as per traditional /etc/passwd lookups. Other fields may also be stored in the userdb, and these are called 'extra fields'. Possibilities are:

chroot: Chroot to given directory. Overrides mail_chroot setting in dovecot.conf.

system_groups_user: Specifies the username whose groups are read from /etc/group (or wherever NSS is configured to taken them from). The logged in user has access to those groups. This may be useful for shared mailboxes.

userdb_import: This allows returning multiple extra fields in one TAB-separated field. It's useful for userdbs which are a bit less flexible for returning a variable number of fields (e.g. SQL).

uidgid_file: Get uid and gid for user based on the given filename.

It's possible to override settings from dovecot.conf (most commonly quota_rule to set per-user quota limits or also plugin-settings).

These fields can be returned the exact same way as uid, gid, and home fields. Below are examples for some user databases.

Overriding settings

Most commonly settings are overridden from plugin section. For example if your plugin section has quota=maildir:storage=1024 value and the userdb lookup returns quota=maildir:storage=2048, the original quota setting gets overridden. In fact if the lookup always returns a quota field, there's no point in having the quota setting in plugin section at all, because it always gets overridden anyway.

To understand how imap and pop3 processes see their settings, it may be helpful to know how Dovecot internally passes them:

Last all the extra fields returned by userdb lookup are used to override the settings. Any unknown setting is placed into plugin {} section (e.g. foo=bar will be parsed as if it were plugin { foo=bar }).

If you want to override settings inside sections, you can separate the section name and key with '/'. For example:

namespace default {
inbox = yes
location = maildir:~/Maildir
}

The inbox setting can be overridden by returning namespace/default/inbox=yes or namespace/default/location=mbox:/var/mail/%u extra field.

LDAP

passwd-file

Below are examples that show how to give two userdb extra fields ("mail" and "quota"). Note that all userdb extra fields must be prefixed with "userdb_", otherwise they're treated as passdb extra fields.